Using OIFS
by nek5000-users＠lists.mcs.anl.gov
08 Aug '11
08 Aug '11
Hi neks,
I'm trying to simulate a turbulent channel flow like in the presentation "A
comparison
of Nek5000 and OpenFOAM for DNS of turbulent channel flow" of Michael A.
Sprague from the last
user meeting (
http://www.mcs.anl.gov/~fischer/nek5000/sprague_nek5000_dec2010.pdf
"mid"-case).
In the presentation it is mentioned that the CFL number is approx. 2 so I
have choosen the BDF3/OIFS3
scheme. However the solution blows up and Nek5000 stops the computation
after 49 steps.
Are there any parameters I have to set in the rea-file to get it work? TCHAR
is true and p026 is
set to 3. Dealiasing is turned on as well, but I'm not sure if the weight of
the filter may be wrong.
The files of the case are attached.
Thanks!
Alex
Hi,
I am a new to NEK and I am trying to run a few examples for my OS scaling
experiments. I went through the manual which is at:
http://www.mcs.anl.gov/~fischer/new.pdf. In the chapter that speaks about
a basic problem setup, there is a line in the 'Memory Requirements'
section that says:
Total Memory Required for simulation = E(N +1)^3 points × 400(wds/pt) ×
8bytes/wd
I have been playing around with the SIZE file a little bit and adjusting,
lx1, lelt, lxd, lp and lelg parameters. However I am unable to find where
I can adjust 'E' from the equation. I understand that 'lelt' is maximum
elements per processor and 'lelg' is maximum elements per simulation? Is
'lelg' same as 'E'? is 'lelt = lelg / nprocs' ? I assumed that 'E = lelg'
and changed 'lelg' for 'timing' example to run it on a 4096 node
configuration (1 rack of BG/P:Intrepid in VN mode). I keep getting the
error:
Too many processors ( 4096 ) for to few elements ( 512 )
... and the value 512 does not seem to change although I have changed
'lelg' and run 'makenek timing'. Is the value of 'E' picked up from the
.re2 file? Would I have to generate it using 'genbox' after I change some
other configuration?
I understand that NEK has been scaled upto 40 racks of Intrepid at
Argonne. I am also trying to run experiments of upto 32 racks if possible.
But I want to get started with smaller runs. Is there a repository of
configurations or tarred files where I could get larger, successfully run
problem instances?
Thanks.
Regards,
Harish Naik
Predoctoral Appointee
Mathematics & Computer Science Division
Argonne National Laboratory
P: (630) 252-2029
W: http://www.mcs.anl.gov/~hnaik
